The MPL Reference Manual: BOOST_MPL_AUX_LAMBDA_SUPPORT

BOOST_MPL_AUX_LAMBDA_SUPPORT

Synopsis

#define BOOST_MPL_AUX_LAMBDA_SUPPORT(arity, fun, params) \
    unspecified token sequence \
/**/

Enables metafunction fun for the use in Lambda Expressions on compilers that don't support partial template specialization or/and template template parameters. Expands to nothing on conforming compilers.

Header

#include <boost/mpl/aux_/lambda_support.hpp>

Parameters

Parameter	Requirement	Description
`arity`	An integral constant	The metafunction's arity, i.e. the number of its template parameters, including the defaults.
`fun`	A legal identifier token	The metafunction's name.
`params`	A PP-tuple	A tuple of the metafunction's parameter names, in their original order, including the defaults.

Expression semantics

For any integral constant n, a Metafunction fun, and arbitrary types A1,... An:

template< typename A1,... typename An > struct fun
{
    // ...

    BOOST_MPL_AUX_LAMBDA_SUPPORT(n, fun, (A1,...An))
};

Precondition:	Appears in `fun`'s scope, immediately followed by the scope-closing bracket (`}`).
Return type:	None.
Semantics:	Expands to nothing and has no effect on conforming compilers. On compilers that don't support partial template specialization or/and template template parameters expands to an unspecified token sequence enabling `fun` to participate in Lambda Expressions with the semantics described in this manual.

Example

template< typename T, typename U = int > struct f
{
    typedef T type[sizeof(U)];

    BOOST_MPL_AUX_LAMBDA_SUPPORT(2, f, (T,U))
};

typedef apply1< f<char,_1>,long >::type r;
BOOST_MPL_ASSERT(( is_same< r, char[sizeof(long)] > ));

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